Gamma Titanium Aluminides are a promising class of lightweight high temperature alloys exhibiting higher specific strength up to 800°C as nickel based superalloys in use today. The main hurdle hindering their adoption is their low ductility that reduces damage tolerance in operation and increases difficulty during processing, i.e. making most casting processes unsuitable. Because of that additive manufacturing gained traction as a processing route. Laser Metal Deposition, a directed energy deposition process, provides a further design freedom by the absence of a powder bed and enables the fabrication of Functionally Graded Materials. Enabling optimal properties while maintaining lower component weight compared to a monolithic component with one set of “compromise” properties for all sections. This could be used i. e. in an aircraft turbine blade, as the operating conditions change from the hot tip to the cooler blade root. Carefully selected different alloys can be combined that exhibit different microstructures and therefore properties after one common heat treatment.

The first option studied here are two γ-TiAl alloys (TiAl-A: TiAl48Cr2Nb2, TiAl-B: TiAl45Nb4C, at%) of which after heat treatment one shows the so-called duplex configuration enhancing ductility while losing fracture toughness and creep strength compared to the so-called fully lamellar state of the other. These microstructure influences are intensified by the impacts of the alloying elements with chromium enhancing ductility, while the higher niobium content enhances creep properties.
For the relatively small composition changes between TiAl-A and TiAl-B the transition is crack free and tensile and creep tests do not reveal the transition zone as a weak point. Through the comparison of monolithic specimens with multi material ones, we can say that creep properties of multi material specimens are dominated by the weaker TiAl-A in duplex configuration. The only influence of the fully lamellar TiAl-B part of the specimen can be seen in the primary creep stage.

The second option studied is the extension of the composition and property differences from one γ TiAl to the metallic TiAl6V4 (wt%) alloy. The layer wise manufacturing of LMD leads to remelting of previously deposited material and therefore to intermixing even if the powder supply is switched from 100% powder A to 100% powder B. Using the multi material capability a suitable interlayer between the γ-TiAl and TiAl6V4 to circumvent the thermodynamic D019 single phase field, which otherwise would be a weak point, is introduced. Therefore screening experiments how this interlayer should be produced in LMD were conducted. Different number of layers and different powder combinations for these layers were produced and their composition and microstructure analyzed. The mechanical properties investigation is ongoing and will be presented in the talk.